Communication system



Dec. 4, 1945. R. H. CAMPBELL COMMUNICATION SYSTEM 3 Sheets-Sheet 1 Filed Feb. 28, 1944 Dec. 4, 1945.

R. H. CAMPBELL COMMUNICATION SYSTEM Filed Feb. 28, 1944 3 Sheets-Sheet 2 WWW) 3 SheetsSheet 3 v w w m 'R. H. CAMPBELL COMMUNICATION SYSTEM Filed Feb. 28, 1944 v I 1% L F1. w W

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Patented Dec. 4, 1945 UNITED "STATES PATENT OFFICE COM'MUNICATION SYSTELI Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Delaware Application February 28, 1944, Serial No. 524,178

32 Claims. (Cl. 179+s7) The present invention relate to intercommunieating systems and has for its primary purpose the provision of new and improved circuit arrangements for enabling an operator at one station to signal an operator at another, and also for operators at calling stations to obtain a signal as to whether or not the called station is busy or not Another object of the present invention is to provide communication systems with signaling arrangements whereby one station can signal another that it is desired to communicate therewith and wherein the calling station is given different distinctive signals in the event the called station is busy or not busy.

A further object of the present invention is the provision of a new and improved signaling arrangement wherein positive signals are produced at the callingstation that the called station has been conditioned to answer the call.

A further object of the present invention is the provision of signaling arrangements of the character aforesaid which are inexpensive, avoid noise which may be produced by arrangements including relays, and wherein each of the stations of the system is a self-contained unit.

A further object of the present invention is the provision of signaling arrangements of the character aforesaid which are provided with protective fuses and wherein a pair of supply voltages at each station are connected in phase opposition, thereby to reduce the voltage on the system in the event a fuse is blown and to prevent the possibility of sneak currents from operating any of the signal lights under these conditions.

Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the accompanying drawings, in which:

Fig. l is a schematic representation of one embodiment of a signaling system for use with intercommunicating apparatus of the type wherein communication is carried on between stations in opposite directions over separate circuits, and which requires the closure of a selector switch in a transmission circuit to complete that circuit;

Fig. 2 is a similar representation of a modified embodiment of the invention; and

Fig. 3 is a schematic representation of a third embodiment of the invention.

' Reierring now to the drawings, and first to Fig. 1, it may be noted that the system illustrated thereinconsists of three stations, indicated by the reference characters I, 2 and 3. The communication apparatus at the stations has not been illustrated for the reason that the present invention has to do with the signaling arrangements. The communication apparatus may be of any desired type and may be, for instance, of the type disclosed in my copending application Serial No. 457,549, filed September 7, 1942, now Patent No. 2,347,079, granted April 18, 1944, and assigned to the assignee of this application.

It is believed suflicient for the purposes of this application to say that each station may be provided with a microphone connected to the input of an amplifier, a loudspeaker, a transmission circuit, and a reception circuit, and, furthermore, with a communication direction control switch operable to condition the station for reception or transmission. The station is conditioned for reception by connection of the loudspeaker to the reception circuit, and the station is similarly conditioned for transmission by connection of the amplifier output to the transmission circuit which may be connected to the reception circuits individual to other stations by station selector switches. I

In Fig. 1, station I is provided with two station selector switches I. and I2, corresponding to stations 2 and 3, respectively. These switches include the pairs of switch blades I l and I6 adapted to connect the transmission circuit -(the output of the amplifier) to interstation circuits II and 20, also respectively, individual to stations 2 and 3 and constituting the reception circuits for these stations. The reception circuit for station I has not been illustrated, but when the station selector switch correspondingto a desired station has been closed, then communication may be carried on alternately in opposite directions over the reception circuit individual to station I and the transmission circuit for the other station upon alternate operation of the communictaion direction control switches at the two stations.

Stations 2 and 3 are also provided with a number of station selector switches corresponding to the numberof other stations-in thesystem, two in this case. the station selector switches 22 and 24 corresponding to stations I and 3, and station 3 is provided with the station selector switches 26 and 28 corresponding to stations I and 2. If the system included a larger number of stations. then stations in the system would be provided with a correspondingly increased number of station selector switches.

It may be noted that the station selector switches at station 3 are somewhat diflerent from those at stations I and 2. The reason for this Thus, station 2 is provided with system.

will be described in some detail hereinafter. It may be noted also that the transmission circuit closing switch blades for the station selector switches at stations 2 and 3 have not been illustrated. This has been done in order to simplify 3 a description and consideration of the present invention, which, as heretofore stated, has to do onlywith the signaling arrangements.

In accordance with the present invention, the various stations are each provided with a signal light corresponding to every other station in the Thus, station I is provided with signal l thts 33 and 32 corresponding to stations 2 and 3, respectively; station 2 is provided with signal lights 34 and 33 corresponding to stations I and 3, respectively: and station 3 is provided with si nal lights 33 and 43 corresponding to stations I and 2, respectively.

show that the station is being called. The light at the calling station corresponding to the called station remains dark to show that the called station is not busy. When the called station answers, the lights corresponding to the two stations (one at each station) glow steadily. If a third station selects one of the two busy stations, or in the event one station selects a busy station at any time, the lightat the calling station flashes periodically toshow that the called station is busy. Even though the called station is busy, the light corresponding to the calling station thereztlglgws steadily to show that the station is being Each of the stations is provided withits individual voltage supplies, and particularly voltage supplies for producing steady and flashing glow of the lamps. Station I is provided with a flrst transformer 42 providing a steady voltage, and a second transformer 44 coupled with a resistance type flasher unit 43 providing a periodic voltage for producing flashing operation of the lights. Station 2 is correspondingly supplied with transformers 43 and 33 and a flasher unit 32. Station 3, however, is provided with a single transformer 54 having a tapped secondary winding 33 to provide the two voltages. Station 3 is provided also with a resistance type flasher 33.

The resistance type flasher units are actually snap actionswitches operated by an expansible wire. The switches are indicated by the refer- I ence characters 33, and the corresponding wires. by the reference characters 32. When the wires are unheated, they are of a definite length and hold the switches in the positions indicated in the drawings. When current passes through the wires they expand and the switch blades move into their uppermost positions. When this ha pens, the wires cool and the switches snap back into their indicated positions. The flashers may be of standard types available on the market, for instance, they may be of the type manufactured by the Tung-Sol Company of Newark, New Jersey.

I2; and stations 2 and 3 by interstation conductors 14 and 13.

Station selector switch I3 at station I includes the switch blades I3 and 33. The former is connected through conductor 32 to one terminal of the secondary winding of transformer 42 and to the common conductor 34 through a fuse 34. Blade 33 is connected to interstation conductor 33. Station selector switch I2 at station I includes the switch blades 33 and 33.- The former is connected to conductor 32 and the latter to interstation conductor I2.

All the stations in the system are connected by 79 and 3 by interstation conductors l3 and 73 In the indicated position of the selector switches, switch blades 33 and 33 connect conductors 33 and I2 to a conductor 33 through resistors 32 and 34, respectively. Conductor 33 is connected to one terminal of the wire 32 and to switch blade 33, which normally connects conductor 33 to common conductor 34 through conductor 33; In the indicated position of the selector switches, switch blades I3 and 33 connect conductor 32 to resistors 33 and I33, respectively.

" Resistor 33 is connected to conductor 33 and resistor I33 to conductor I3.

Light 33 is connected in series with a resistor I32 across conductor 33- and common conductor 34 by a conductor I34. Light 32 is similarly connected across conductors 34 and 33 through the conductor I34 and resistor I 33.

vOne terminal of the secondary winding oftransformer 42 is connected by conductor I33 to contacts associated with switch blades 33 and 33, and one terminal of the secondary winding of transformer 44 is connected by conductor III to contacts associated with switch blades I3 and 33. The other terminal of the secondary winding of transformer 42 is connected to conductor 32 and to the common conductor through fuse 34. The other terminal of the secondary winding of transformer 44 is connected to wire 32 and by a. conductor 2 to a contact associated with the switch blade 33, so that in the displaced position of the switch blade, the wire 32 is effectively short-circuited to enable it to cool.

Station selector switch 22 at station 2 includes a pair of switch blades I23 and I22. The former is connected to common conductor 34 through conductor I24 and a fuse 34. Blade I22 is connected to interstation conductor 33. Station selector switch 24 includes switch blades I23 and I23. The former is connected to conductor I24 and the latter to interstation conductor I3.

In the indicated positions of the selector switches-at station 2, switch blades I22 and I23 connect conductors 33 and I3 to a conductor I33.

through resistors I32 and I34, respectively. Conductor I33 is connected to one terminal of wire 32 and a switch blade 33 normally connecting conductor I33 to the common conductor through a conductor I33. Switch blades I23 and I23 connect conductor I24 to resistors I33 and I43, respectively. Resistor I33 is connected also to interstation conductor 33 and resistor I43 is connected to interstation conductor I4.

Light 34 is connected in series with a resistor with switch blades I26 and I26. The other terminal of the secondary winding of transformer 43 is connected to conductor I24 and to the commen conductor through a fuse 64, while the other terminal or the secondary winding of transformer E6 is connected to 'expansihle wire 62 and to a normally non-engaged contact of switch 66 by a conductor 552.

The selector switches at station 3 differ from those at stations I and 2 in that a tapped secondary winding 56 is used in place of two transformers; a change requiring the use of an additional switch blade' on .the station selector switches, as will become apparent shortly,

Station selector switch 26 at station 3 includes the switch blades I66, I62 and I64. Switch blade I66 is connected to the common conductor 64 through conductor blade I62 is connected to interstation conductor l6. Switch blade I64 is connected by conductor I63 to one terminal of wire 62 and by branch conductor I'll) to the normally non-engaged contact associated with switch 66.

Station selector switch 26 at station 3 includes the three switch blades I12, I14 and H6. Switch blade I12 is connected to conductor I66 and through fuse 64 to the common conductor 64. Switch blade I14 is connected to interstation conductor I4, and switch blade I16 is connected to the previously mentioned conductor I68.

In the indicated position of the selector switches at station 3, switch blades I64 and I16 are in circuit opening position; switch blades I62 and I" connect conductors I6 and I4 to a conductor I16 through resistors I66 and I62, respectively; switch blades I66 and 2 connect conductor I66 to interstation conductors I2 and I6 through conductor I84 and resistor I66, and conductor I88 and resistor I96, respectively; Conductor I16 is connected to one terminal of wire 62 and the switch blade 66 normally connecting conductor I16 to the common conductor 64 through a conductor I92.

Light 38 is connected across conductors 64 and I2 through conductor I94 and resistor I96. Light 46 is connected across conductor 64 and conductor 16 through the conductor I94 and a resistor I96.

Power at station 3 is supplied by the transformer 54 having a tapped secondary winding 56. The tapped portion corresponds to transformers 42 and 48 at stations I and 2. It is connected by conductor I99 to the normally non-engaged contacts associated with switch blades I64 and I16. The full winding corresponds to transformers 44 and 66 at stations I and 2 and it is connected so that no voltage is applied across them. The connections of the lights at this time are the same, and, therefore, only the connection of light 36 at station I will be described in detail. At station I one terminal of this light is connected to common conductor 64 through conductor I64 and the other terminal is connected to conductor 64 at station 2 through resistor I62, interstation conductor switch blade I22, resistor I32, conductor I36, switch'blade 66, and conductor I36. Resistor 66 is normally connected in parallel with the series connected light 36 and resistor I62 I66 and fuse 84. Switch,

by conductor I99A to the normallynon-engaged contacts associated'with I14.

As heretofore indicated, all the lights in the system are normally deenergized; when one station calls another and the other is not busy, then the light at the first station corresponding to the second remains deenerglzed while the light at the second corresponding to the first glows steadily; when the second answers the first, the above specified lights at both stations glow steadily; and when a third station selects one of the two busy ones, the light at the third station corresponding to the called station flashes periodically to indicate that the called station is busy and the light at the called station corresponding to the calling station .glows steadily.

Undernormal conditions both terminals of all lights are connected to the common conductor switch blades I62 and through switch blade I6, conductor 82 and fuse 83.

When one station calls another that is not busy, the light at the calling station remains deenergized, and the light at the called station is continuously energized and glows steadily. This operation will be described in connection with a call from station E to station 2. For station I to call station 2, it is necessary that the station selector switch I6 be operated to its displaced position. This operation effects the closure of switch I4, thereby to complete the connection ofthe transmission circuit to the reception circuit I6 individual to station 2. It also eflects the connection of light 34 at station 2 (which corresponds to station I) to the secondary winding of transformer 42 so that the light 34 glows. The energizing circuit for light 34 extends from one terminal of the secondary winding of transformer 42 to the other through the following circuit: conductor I66, switch blade 86 in its displaced position, conductor 66, resistor I42, light 34, conductor I44, conductor 64, and fuse 84. Resistor I38 is at this time parallel to the light 34 and resistor I42, but the light is energlzed sumciently to be lighted because of the parallel connection. The operation of selector switch I6 also removes from circuit, at station I, resistor 68 normally connected parallel to light 36 and resistor I62, but this does not afiect the energization of light 36.

The operation of selector switch I6 also results inthe periodic energization of conductor I2 so that if a station other than the called station selects station I, the calling station will be given flashing signal to indicate the station is busy. This operation will be described in detail hereinafter.

.When station 2 responds to the call, selector switch 22 is operated into its displaced position, thereby to elfect the energization of light 36 at station I, so that it, too, glows steadily. The light 36 is connected across the secondary winding of transformer 46 through the following circuit: conductor I48, switch blade I22 in its displaced position, conductor 66, resistor I62, light 36, conductor I64, and the common conductor 64. Operation of switch 22 also removes from circuit the parallel connected resistor I38,- but this does not affect the energization of light 34.

As a result, when two stations (or more) are to station 2 would flash periodically.

It may be worth while to mention that when the selector switch 22 at station 2 is operated, the reception circuit individual to station I is. connected to the transmission circuit of station 2. Thereafter, communication may be carried on between the stations, as, for instance, by alternate operation of communication direction control switches at the two stations, pursuant to the disclosure of my copending application Serial No. 457,549. If desired, the system may be arranged so that communication may be car -ried on after closure of the station selector switches without subsequent manipulation of any communication direction controlling switches.

If a third station should select one of the two stations that are in communication with each other, then the light at the third station correspending to the called station flashes periodically,

whereas the light at the called station corresponding to the calling station glows steadily to indicate that another station desires to communicate with it. 4

When a station selector switch is operated at any station, for instance, the station selector switch It at station I, a voltage is periodically applied to conductors leading to station I lights at stations other than the selected one (here conductor 12) by the resistor type flasher (here switch 46). When the switch It is operated, a circuit is completed through the wire 02, and when the latter becomes heated. the switch 60 is snapped into its displaced position to shortcircuit wire 02. The wire then cools and switch blade It returns to its initial position. The wire s: is energized in the indicated position of switch It by connection across the secondary winding of transformer 44 through the following circuit: conductor IIII, switch blade ll in its displaced position, conductor 02, fuse ll, conductor 64, conductor l6, and switch blade ll. When the switch blade is in its indicated position, no voltage is applied to interstation conductor 12 as it is connected'to conductor 04 through switch blade ll, resistor 24, conductor ll, switch blade II, and conductor 86. However, when the switch blade is in its displaced position, secondary winding of transformer 44 is connected across interstation conductor I2 and the common conductor ll.

When the station selector switch 20 at station 3, corresponding to station I, is in its indicated position, the light It at station I does not glow even though it is connected to conductor 12 ind conductor 12 is periodically supplied with voltage. This results from the parallel connection of light 32 and resistor I" with resistor l and the series connection of this parallel circuit with resistor 84 across the secondary winding of transformer 44. However, when switch 28 is operated at station I to call station I, then the resistor I86 is removed from circuit and the secondary winding of transformer 44 is connected across a series circuit including resistor 94, conductor 12, resistor I98 and the light 3'. As a result, an increased voltage is placed across the light sufllcient to eifect its energization, which is periodic beductor I", switch blade I in its displaced position, conductor Ill, expansible wire '2, switch blade-60, conductor I02, common conductor is and fuse 84. Each time the expansible wire is short-circuited by switch 80 engaging conductor I'll, the interstation conductor 14 leading from station 3 to station 2 is connected to the tapped portion of the secondary winding through the series resistor "2 so that voltage is applied to light II at station 2 (correspondingtc station I), but it is not energized sumciently to glow.

The signal lights may be of any desirable form and they and the resistors may have any desirable values such as to provide the operation heretofore described. For instance, the lights may be of the neon tube type (as or the type NE 17 manufactured by the General Electric Company), resistors l2, I4, I32, I, III and I82 may have values oi about 2,000 ohms, resistors I02,

Ill, I42, I, I and Ill may have values of about 1,000 ohms, and resistors II, III, III, I, I" and I may have values of about 3,000 ohms.

The voltages across the secondary windings of transformers l2 and 44 and of transformers It and II are connected so that they are 180 out of phase. The secondary windings oi transformers u and ll may have a voltage of about 70 volts 4. tion I calling station 2, station 2 answering stacause of the periodic application of voltage to conductor 12,

When station 3 selects station I by'operation of selector switch 28, light 32 at station I is continuously energized and glows steadily. The light is connected across the secondary winding 58 ondary winding It, the circuit including con- 7 and 3,

station that it is being called and an indication at the calling station that the called station is not busy. When the called station answersfthe two lights remain energized. When a third station calls either one or the other of the two stations in communication with each other, the light at the third station corresponding to the called statiolrli flashes periodically while the light at the ca ed station correspondin to the calling tion glows steadily. 8 8

The system illustrated in Fig. 2: includes three stations indicated by reference characters I, 2 and I. The system may, however, comprise more stations, and the communication apparatus, which has not been illustrated, may take various forms, as set forth above in connection with the description of the apparatus of Fig. 1.

Each of the stations is provided with station selector switches corresponding to other stations in the system. Thus, station I is provided withv station selector switches Ill and 2.2 corres nding to stations 2 and I, station 2 with sefe ctor switches 2N and 2" corresponding to stations I and station 8 with selector switches Ill and 210 corresponding to stations 1 and 2. Each of the selector switches includes (in addition to the communication circuit controlling switch 14, shown only with switch 260) a pair of switch blades indicated by the reference character applied to the switch followed 'by the suffixes 1 and 2.

Each of the stations is also provided with signal lights corresponding to the other stations in the system. Thus, station I is provided with signal lights 212 and 214, station 2 with signal lights 216 and 216, and station 3 with signal lights 220 and 222. The stations are provided with transformers 224, 226 and 226, respectively, the secondary windings of which are of the tapped type. The stations are provided also with resistance type flasher units 230, 232 and 234, respectively, each of which includes a switch 60 and an expansible wire 62.

The system includes a number of interstation conductors as follows: a common conductor 236; conductors 238 and 240 between stations I and 2; conductors 242 and 244 between stations I and 3; and conductors 246 and 246 between stations 2 and 3. 1

Under normal conditions, when no station selector switches are operated, the 'lights 01' the system are deenergized. The light at each station corresponding to another station is normally connected to'the secondary winding of the transformer at the other station, but it. is not energized suiiiciently to be lighted because his connected in parallel with one resistor and in series with another resistor. Thus, the light 212 at station 1 is normally connected in parallel with a resistor 250, and the parallel connected resistor and light are connected in series with a second resistor 252. Incidentally, the light 212 is connected in series with another resistor 254, the light and resistor 264 being paralleled by the resistor 250. The light 212 and resistor 254 are connected across the conductors 236 and 236 by a conductor 256. Resistor 250 is normally connected across the same two conductors through the switch blade 200-2 and conductor 256. Conductor 238 is connected to resistor 252 through switch blade 204-1, and thence to secondary winding of transformer 226 through conductor 260 and switch 60.

Light 214 at station 1 corresponding to station 3 is similarly normally connected to the secondary winding of transformer 228 through the series resistor 262 and in parallelwith a resistor 264. The resistor 264 is connected across conductors 236 and 242 by conductor 256 and switch blade 202-2. Resistor 262 is connected to conductor 242 by the switch blade 208-1 and to the transformer winding through conductor 266 and switch 60.

Light 216 at station*2 corresponding to station 1 is normally connected to the secondary winding of transformer 224 at station I through the series resistor 268, and it and its series resistor 210 are paralleled by the resistor 212. The light is connected across conductors 236 and 240 through the resistor 210 and conductor 214. The light 216 and resistor 210 are paralleled by the resistor 212, th parallel circuit including switch 204-2 and conductor 216. The energizing circult for the light includes the interstation conductor 240, switch blade 2110-1, the resistor 268, conductor 218, switch 60, and the common conductor 236.

Light 216 at station 2 corresponding to station 3 has associated with it a series resistor 260, the

light and this resistor being connected in parallel with resistor 262, and this parallel circuit is connected to the secondary winding of transformer 226 at station 3 through the series resistor 284. Light 216 and resistor 280 are connected across conductors 236 and 246 through the previously mentioned conductor 214. Resistor 262 is connected across the same conductors through switch blade 206-2 and conductor 216. The circuit to the transformer winding includes conductor 246, switch blade 210-1, resistor and switch 60.

Light 220 at station 3 corresponding to station 1 and its associated resistor 266 are normally connected in parallel with resistor 268, and the parallel circuit is connected to the secondary winding of transformer 224 at station I through interstation conductor 244 and a series resistor 290. Light 220 and resistor 266 are connected across conductors 236 and 244 through conductor292. Resistor 266 is connected across the same conductors through switch 206-2 and conductor 234.

The parallel circuit is connected to the secondary winding of transformer 224 through conductor 244, switch blade 202-1, resistor 290, conductor 216. and switch 60.

Light 222 at station 3 corresponding to station 2 and its associated resistor 266, which are connected in parallel with resistor 293. are normally connected to the secondary winding of transformer 226 at station 2 through interstation conductor 246, switch blade 266-1, resistor 3013, conductor 260, and switch 150. Resistor 266 is paralleled with the light 222 and resistor 296 through a circuit including switch 2 I 0-2 and conductor 264.

Under normal conditions a periodic voltage is not applied to any of the interstation conductors, but when a-selector switch at a station is oper ated, then a periodic voltage is applied to interstation conductors leading from that station to stations other than that for which the station selector switch was operated. Thus, when the station selector switch 200 at station 1 corresponding to station 2 is operated, the flasher switch 230 is rendered operative periodically to apply voltage to interstation conductor 244 leading to the station number 1 light 222 at station 3 (andsimilarly to other stations if more stations are included in the system).

When switch 200 is operated, the expansible wire 62 is connected across the secondary winding of transformer 224. The circuit includes conductor 256, switch 200-2 in its displaced position, conductor 302, the wire 62 and switch 60. It should also be noted that at the same time switch blade 200-1 connects the tapped portion of the secondary winding of transformer 224 to the interstation conductor 240 through conductor.304, so that the light 216 at station 2 is energized continuously and sumciently to cause it to glow as a resultofthe elimination of the series resistor 266 from the energizing circuit for the light. Stations 2 and 3 are provided with conductors 306 and 306, respectively, to perform the functions performed by the conductor 304 at station 1. This operation will be described in greater 284, conductor 266.-

The wire is short-circuited by the and 4. Each is provided with station selector switches corresponding to other stations in the system. Thus, station is provided with selector switches 406, 402 and 364 corresponding to stations 2, 3 and 4, respectively; station 2 is provided with selector switches 466, 466 and 4H! corresponding to stations I, 3 and 4, respectively; station 3 ls'provlded with selector switches 2, M4 and 6 corresponding to stations I, 2 and 4, respectively; and station 4 is provided with selector switches H8, 420 and 422 corresponding to stations 8, 2 and 3, respectively. Each of the switches includes a pair of switch blades indicated by the reference character applied to the switch followed by the suilixes I and 2, respec tively. Each also includes a transmiss on circuit controlling switch like the one I4 shown in conjunction with switch 466 at station I and oper able in the manner described in connection with 3116 embodiment of the invention illustrated in Each of the stations in the system also includes a signal light corresponding to the other stations in t e system. Thus. station 9 is provided with signal lights 424, 426 and corresponding to stat ons 2. 3 and 4; station 2 is provided with signal lights 430, 432 and 434; station 3 with signal lights 436, 438 and 446; and station 6 with signal lights 442, 644 and 446.

Power is su plied to the signal circuits by transformers 446. 4513, 462 and 454 at stations i, 2, 3 and 4, respectively. The stat ons also include resistance type flasher units 453, 458, 466 and 462, respectively, each of which includes the switch 66 and the expansible wire 62.

T e system also includes a number of interstation conductors, one or" which is the common conductor 464, and others extending from the signal lights at the various stations to the stations corresponding to the signal lights. Thus, conductors 466 and 466 extend between stations I and 2; conductors 416 and 412 extend between stations l and 3; conductors 414 and 416 extend between stations l and 4; conductors 418 and 486 extend between stations 2 and 3; conductors 482 and 464 extend between stations 2 and 4; and conductors 486 and 43% extend between stations 3 and 4.

Wren no selector switches have been operated, the lights are all deenergized, both terminals of each light be ng connected to the common conductor 464. The circuits for thus connecting the lights to the common conductor each include a conductor 496-I, 496-2, 490-3, and 496-4, at the stations indicated bylthe sufllx, the light, the

corresponding interstation conductor, a series re-' sistor 492 (all of which have been indicated by the same reference character for the purpose of simplicity), a selector switch blade having the suflix 2, a conductor 494 followed by the sufiix corresponding to the station, the switch blade 60, and a conductor 496 followed by the sufilx corresponding to the station.

When one station calls anothenthe secondary winding of the transformer at the calling station is connected to the interstation circuit leading to the light at the called station by the selector switch blade having the sumx 2, the connection to the transformer being effected through a conductor 496 followed by the suiiix corresponding to the station. At the same time, the selector switch blade'followed by the suffix I connects the resistance flasher unit to the transformer through a circuit including the conductor 56!! followed by the suillx corresponding to the station.

In the operation of the system of Fig. 3 the lights are normally deenergized as both terminals of each is connected to the common conductor. When one station calls another and the other is not busy, then the light at the called station corresponding to th calling station glows steadily, while the light at the calling station corresponding to the called station remains dark. At the same time lights corresponding to the calling station at the other stations in the systemflash periodically. When the second station answers the first, the light at the first station corresponding to the second also glows steadily, and the lights for both the calling and called stations flash periodically at other stations in the system. When a third station selects one of the two busy ones, the light at the third station corresponding to the busy one called continues to flash periodically while the-light corresponding to the third station at the called busy station glows steadily. Lights at stations in the system other than the two busy ones and the third station, and corresponding to all three stations, flash periodically.

Under normal conditions, the lights at the stations have both terminals connected to the common conductor through similar circuits. For this reason it is deemed necessary to describe but one circuit and this will be done in connection with the light 4124 at station I corresponding to station 2. One terminal of the light is connected to the common conductor 464 through conductor 4964. The other terminal is connected to the common conductor through interstation conductor 466, resistor 492, switch blade 406-2, conductor 494-2, switch 66 and conductor see-2.

When one station calls another that is not busy, the light at the called station corresponding to the calling station glows steadily, the light at the calling station corresponding to the called remains dark, and lights at the other stations in the system corresponding to the calling station flash periodically. Assuming that station I calls station 2, then station selector switch 400 is operated to its displaced position to connect light 436 at station 2 (corresponding to station -I) to the secondary winding of transformer 446 and also to energize the resistance flasher unit 456 so that lights 436 and 442 corresponding to station I at stations 3 and 4, respectively, will flash periodically. Light 436 is connected to the transformer through a circuit including conductor 498-I, switch blade 400-2, resistor 432, interstation conductor 466 leading to the light, conductor 496-2 and the common conductor 464. The flasher is energized through a circuit including the conductor 498-l, switch blade Mill-I,

conductor BOO-I, the expansible wire 62, switch blade 66, conductor 496-I and the common conductor 464. Wire 62 is thus heated but at this time no voltage is applied to interstatlon conductors 4'52 and 416 leading to lights 436 and 442, because they are connected to the common conductor. When switch 66 is operated as a result of the heating of wire 62, the wire is shortcircuited and the secondary winding of. transformer 458 is connected across lights 436 and M2. Light 436 is connected across the. transformer through a circuit including conductor 498-I, switch blade 4IlB-I, conductor 560-I, switch 66 in its displaced position, conductor 494-I, switch blade 462-I, resistor 492, interstation conductor 412 leading to the light 436, conductor 490-3 and the common conductor 464.

In similar manner the light 442 at station 4 corresponding to station I is energized through switch blad 464-2, resistor 462 and interstatlon conductor 416 leading to station 4.

When station 2 responds to the call, selector switch 406 is operated thereby to eiiect continuous energization of light 424 at station I corresponding to station 2, and also the periodic flashing of lights 436 and 444 at stations 8 and 4 connected to the secondary winding of transformer 460 through circuits including switch blades 406-2 and 4iil2 in a manner deemed to be clear from the description oi the operation of apparatus at station I.

In the event station 3 should now select either station I or station 2, say station 2-,then upon operation of station selector switch 4, light 432 at station 2 is energized continuously while lights 426 and 446 at stations I and 4 corresponding to station 3 flash periodically. The circuits for the steady and periodic energization of the lights are like those previously described and the circuits will, therefore, not be described in detail. It isbelieved sufllclent to state that light 482 is energized through a circuit including switch blade 4-2 and interstation conductor 41!. Flasher 460 is energized through switch blade 4i4-i and periodic voltages are applied to lights 426 and 446 through circuits including switch blade 4-2 and interstation conductor 4", and switch blade 4i62 and interstation conductor 4, respectively.

From the foregoing detaileddescription oi the invention, it may be noted that it has a number of advantages including those now about'to be reviewed briefly. In the first place, all of the equipment, including the voltage supplies. areself-contained in the units at each station. Thus. 1

installatidn 01' a station is. greatly facilitated and a system may be made to include a desired number 01 stations with ease. The flasher type periodic voltage supply means does not include anyrelays, thereby minimizing expense and reducing excessive noise made by a relay. In'appliratus oi the character to which this invention pertains, the microphone is 01 necessity located quite close to the power supply and the use of a flasher type voltage supply reduces the noise level. Distinctive signals are produced at the calling and called stations and at other stations inthe event a busy station is selected. A steady and positive signal is produced at the called station and when the" calling station answers, a similar signal-is produced at the station originating the call. Other stations are given diiterent distinctive s'gnals denoting that a station which they may desire to call is busy, thereby facilitating the ascertainment of the condition oi any station in the system.

While only three embodiments of the invention have been described'in detail, it should be understood that the details oi the circuits are I not to be construed as limiting the invention except insofar as set forth in the accompanying claims.

Having thus described claim as new and desire to secure by letters Patent'ot the United States is: V g

my invention, what I 1. In a multiple station intcrcommunicating system, the combination including, signal lights at each station corresponding to other stations in the system. station selector switches at each station corresponding to other stations in the system, and means including signal light circuits between the stations and light circuitcontrolling switches operable with said selectorswitches constructed and arranged to produce intermittent glowing oi the light at the selecting station and continuous glowing of the light at the selected station when a selector switch at the selecting station corresponding to the selected station and a selector switch at the selected station corresponding to some other station have been operated.

2. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, and means including signal light circuits between the stations and light circuit controlling V switches operable with said selector switches upon operation of the latter to select a station for producing steady glowing oi the signal light at a selected station and for producing intermittent glowing oi the light atthe selecting station in the event a station selector switch corresponding to a station other than the selecting station has been operated at the selected station.

3. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, a source of steady voltage at each station, a source of intermittent voltage at each station, and means including signal light and power circuits between the stations and circuit controlling switches operable with said selector switches upon operation of the latter to select a station for eil'ecting the connection 01' the signal light at a selected station to a source oi steady voltage and for eil'ecting the connection oi the light at the selecting station to a source 01 intermittent voltage in the event a station selector switch corresponding to a station other than the selecting station has been operated at the selected station.

4. In a -multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system. station selector switches at each station corresponding to other stations in the system, a source oi steady voltage at each station, a source of intermittent voltage at each station, and means including nal light and power circuits between the stations and circuit controlling switches operable with said selector switches upon operation of the latter to select a station for electing the connection of the ignal light at a selected station to the source of steady voltage at the selecting station and for eKecting the connection oi the light at the selecting station to the source oi intermittent voltage at the selected station in the event a station selector switch corresponding to a station other than the gifting station has been operated at the selected 5. In a multiple station intercommunicating system, the combination including, signal means asoaaosi sponding station have not been operated and for producing intermittent operation of the signal means at the first station and continuous operation of the signal means at the corresponding station in the event switch means corresponding to a station other than the first station has been operated at the corresponding station.

6. In a multiple station intercommunicating system, the combination including, signal means at each station corresponding to other stations in the system, switch means at each station corresponding to other station in the system, a source of steady voltage at each station, a source of intermittent voltage at each station, and means including signal and power circuits between the n stations and circuit controlling switches operable with said switch means upon operation of the lat- 1 ter at a first station for connecting the signal light at a corresponding station to said source of steady voltage and for connecting the light at the first station to a source of intermittent voltage and the signal light at the corresponding station to said source of steady voltage in the event switch means corresponding to a station other than the first station has been operated at the corresponding station.

'7. In a multiple station intercommunicating system, the combination including, signal lights conductor and said windings being connected thereto so as to be 180 degrees out of phase.

9. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, a first and steady voltage source at each station, a second volt ge source at each station normally connected tolights at other stations corresponding to the station, said connections inglowing thereof at each station corresponding to other stations in the system, station selector switches at each 1 station corresponding to other stations in the system, a first and steady voltage source at each station, a second and periodic voltage source at each station, and means including signal and power circuits between the stations and circuit controlling switches operable with said selector switches upon operation of the latter to select a station for connecting the signal light at a selected station to the steady voltage source at the selecting station and eflecting steady glowing thereof and for connecting the light at the selecting station to the second voltage source at the selected station and effecting periodic glow ing thereof in the event a station selector switch corresponding to a station other than the selecting station has been operated at the selected station.

8. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station'selector switches at each station corresponding to other stations in the system, a transformer winding providing a first and steady voltage source at each station, a transformer winding and a resistance type flasher unit at each station providing a second and periodic voltage source at each station, and means including signal and power circuits between the stations and circuit controlling switches operaole with said selector switches upon operation oi. the latter to select a station for connecting the signal light at a selected station to the said first winding at the selecting station and effectin steady glowing thereof and for connecting the light at the selecting station to the second winding at the selected station and effecting Periodic lowing thereof in the event a station selector eluding resistance means preventing glowing of the lights, each station including also means operable upon operation of the selector switches and associated with the second voltage source for producing a periodically recurring voltage, and means including signal, resistance means, and power circuits between the stations and circuit controlling switches operable'with said selector switches to select a station for connecting the signal light at a selected station to the steady voltage source at the selecting station and efiecting steady glowing thereof and for connectingthe light at the selecting station to the periodically recurring voltage at the selectedistation and'eflecting periodic in the event a station selector switch corresponding to a station other than the selecting station has been operated at the selected station.

10. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, a first and steady voltage source at each station, a second and periodically recurring volt age source at each station, said sources at each station including the and means including signal and power circuits between the. stations and circuit controlling switches operable with said selector switches upon operation of the latter to select a station for connecting the signal light at a selected station to said transformer winding at the selecting station and effecting steady glowing thereof and for pcriodically connecting'the light at the selecting station to said transformerwinding at the selected station and effecting, p riodic glowing thereof in theevent a station se ector switch corresponding to a station other than the selectin station has been operated at the selected station. I

11. In si naling apparatus for use in communication systems of the type lector switches, the combination including, normally inoperative means adapted when rendered operative to produce a periodically recurring voltage, and switch means operable with said selector switches for rendering operative said voltage producing means when the selector switches are operated to select a station.

- the selector switches are operated to select a switch corresponding to a station other than the selecting station has been operated at the selected station, said power circuits including a common station. v

13. In signaling apparatus for use in communication systems of the type having station selector switches and signal circuits, the combination insame transformer windin f having station seincluding, normally ineluding, normally inoperative means adapted when rendered operative to produce a periodically recurring voltage, said means including a transformer winding having a pair of terminals, one of which is normally disconnected, an expansible wire connected to the other terminal of said winding, a conductor, and a two-position switch adapted normally to connect said wire to said conductor and operable upon heating of the wire to short-circuit the wire and disconnect the wire from said conductor, switch means operable with the selector switches norma ly connecting said conductor to the signal circuits, and other switch means operable with said selector switches for completing a circuit through said conductor, wire and windin when the selector switches are operated to select a station to efiect periodic operation of said two-position switch and the periodic application of voltage to said signal circuits.

14. In sigralng apparatus for use in communication systems of the type having station selector switches and signal circuits, the combination including, normally inoperative means adapted when rendered operative to produce a periodically recurring voltage, sad mears including a conductor, a transformer winding having a pair of terminals and a terminal tap, one of said terminals being connected to the conductor and said tap being normally disconnected, an expansible wire and a two-position switch connected to one terminal of the wire and adapted normally to adapted when rendered operative to produce a periodically recurring voltage for energizing lights at other stations, said means including a transformer winding having a pair of terminals, one of which is normally disconnected, an expansible wire connected to the other terminal of said winding, a conductor common to all stations, and a two-position switch adapted normally to connect said conductor to said wire and operable upon heating of the wire to short-circuit the wire and disconnect the wire from said conductor, switch means operable with the selector switches normally connecting said conductor to signal circuits connected to lights at other stations corresponding to the station, and other switch means operable with said selector switches for completconnect said other terminal of the winding to the signal circuits and operable upon heating of the wire to connect the wire to said conductor and open the circuit to the winding. switch means operable with the selector switches normally connecting 'the said switch to signal circuits, and other switch means operable with said selector switches for connecting said wire to said conductor when the selector switches are operated to select a station to effect periodic operation of said two-position switch and the periodic application of voltage to said signal circuits.

-15. In a multiple station communication system of the type wherein each station has station selector switches and signal lights corresponding to other stations in the system, the combination including, normal y inoperative means at each station adapted when rendered operative to produce a periodically recurring voltage for energizing lights at other stations, and switch means operable with said selector switches for rendering operative said voltage producing means when the selector switches are operated to select stations.

16. In a multiple station communication system of the type wherein each station has selector switches and signal lights corresponding to other stations in the system, the combination including, norma ly inoperative means at each station adapted when rendered operative'to produce a periodically recurring voltage for ener izing lights at other stat'ons, switch means operable with the selector switches normally connecting said voltare producing means to signal circuits connected to lights at other stations. and other switch means operable with said selector switches for rendering operative said voltage producing means when the selector switches are operated to select a station.

1'7. In a multiple station communication system of the type wherein each station has selector switches and signal lights corresponding to other stations in the system, the combination including. normally inoperative means at each station irg a circuit through said conductor, wire and winding when selector switches are operated to eiTect periodic operation of said two-position switch and the periodic application of voltage to said signal circuits. v

18. In a'multiple station communication system of the type wherein each station has selector switches and signal lights corresponding to other stations in the system, the combination including, normally inoperative means at each station adapted when rendered operative to produce a periodically recurring voltage for energizing lights at other stations, said means including a conductor common to all the stations, a transformer winding having a pair of .terminals and a terminal tap, one of said terminals being connected to the conductor and said tap being normally disconnected. an expansible wire, and a two-position switch connected to one terminal of the wire and adapted normally to connect said other ter- ,minal of the winding to signal circuits leading to other stations and operable upon heating of the wire to connect said wire tosaid conductor and open the circuit to the winding, switch means operable with the selector switches normally connecting said two-position switch to the signal circuits, and other switch means operable with said selector switches for connecting said wire to said conductor when the selector switches are operated to select a station to effect periodic operation'of said two-position switch and a periodic application of voltage to said signal circuits.

19. In signaling apparatus for use in communication systems of the type comprising stations each having station selector switches and signal lights corresponding to other stations in the sysresistor ior' each light, a light energizing circuit including a resistor adapted to be connected to lights at other stations. and switch means operable with the selector switches normally rendering said voltage producing means inoperative and connecting said resistor in shunt with respect to its associated light and operable when the selectorswitch is operated to render the voltage supplying means operative to supply Said i ht ircuits with, periodically recurring voltage and to disconnect said resistor from the light.

20. In signaling apparatus for use in communication systems of the type comprising a plurality of stations each having station selector switches and signal lights corresponding to other stations in the system,.the combination including, a shunt resistor for each light, light energizing circuits including a resistor'and extending from stations to lights corresponding to the station at other stations, and switch means operable with the selector switches normally connecting said shunt v (resistors in shunt with respect to its associated lights at other stations, and switch meansoperable with the selector switches normally rendering said voltage producing means inoperative and connecting said resistor in shunt with respect to its associated light and operable when the selector switch is operated to render the voltage supplying means operative to supply light circuits other than that corresponding with the operated selector switch with periodically recurring voltage, to disconnect said resistor from the light, and to supply the light circuit corresponding to the operated selector switch with a steady voltage.

22. In a multiple station communication system of the tyne wherein each station has station selector switches and signal lights corresponding to other stations in the system, the combination including. normally inoperative means at each station ada ted hen rendered operative to produce a periodically recurring voltage, a shunt resistor for each light. a light energizing circu t including a resistor extending from'each station to lights corres onding to that station and other stations of the system. and switch means operable with the station selector switches normally rendering said voltage producing means inoperative and connecting a resistor in shunt with the light corresponding to the station corres onding to the station selector switch and operable when the selector switch is operated to render the voltage supplying means operative to supply light circuits with periodically recurring voltage and to disconnect the associated resistor from circuit with the associated light.

23. In multiple station communication systems of the type wherein each station includes station selector switches and signal lights corresponding to other stations in the system, the combination including, a shunt resistor for each light, a light energizing circuit including a resistor extending from each station to lights corresponding to the station at other stations in the system. and switch the light corresponding to the station associated with the selector switch,and operable when the selector switch is operated to render the voltage supplying means operative to supply light circuits other than that corresponding with the operative selector switch with periodically recurring voltage, to disconnect said resistor fromthe light, and to supply the light circuit corresponding to the operated selector switch with a steady voltage.

' 25. In a multiple station communication system, the combination including, signal lights at each station corresponding to other stations-in the system, station selector switches at each station corresponding to other stations in the'system, and means including signal light circuits between the stations and light circuit controlling switches operable with said selector switches upon operation of the latter to select a station for producing intermittent glowing of the lights at stations other than the selected station.

26. In a multiple station communication sys tem, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, a voltage source at each station providing a periodically recurring voltage, and means including signal light and power circuits between the stations and circuit controlling switches operable with said selector switches upon operation of the latter to select a station for connecting the lights means operable with theselector switches normally connecting resistors in shunt to lights associated with stations corresponding to the selector switch and operable when the selector switch is operated to disconnect said resistor from circuit with the light. I

24. In a multiple station communication system of the type comprising a plurality of stations each having station selector switches and signal lights corresponding to other stations in the system, the combination including, normally inoperative means at each station adapted when rendered operative to produce a periodically recurring voltage, a shunt resistor for each light, a light energizing circuit including a resistor adapted to be connected to lights corresponding to the station at other stations, and switch means operable with the selector switches normally rendering said voltage producing means-inoperative and connecting an associated resistor in shunt to at stations other than the selected station to said voltage source. 1

27. In a multiple station communication system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, normally inoperative means at each station for providing a periodically recurring voltage, and means including signal light and power circuits between the stations and circuit controlling switches operable with said selector switches upon operation of the latter tosele'ct a station for rendering said voltage. providing means operative and for connecting the lights at stations other than the selected station to said voltage providing means.

28. In a multiple station communication system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, and means including signal light circuits between the stations and light circuit controlling switches operable with said selector switches upon operation of the latter to select a station for producing steady glowing of the signal light at a selected station andfor producing intermittent glowing of the lights at stations other than the selected station.

29. In a multiple station communication system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations in the system, means providing a steady voltage at each station, normally inoperative means providing a periodically recurring voltage at each station connected to the. lights corresponding to the station at other stations, and means including signal light and power circuits between the stations tem, and means including power supplying means and power and signal light circuits between the stations and power and light circuit controlling switches operable with the selector switches for producing a steady glow of the light at the called station corresponding to the calling station upon operation of the called stationselector switch at the calling station and for producing a steadyglow of the called station light at the calling station upon operation of the calling station selector switch at the called station, thereby to give a positive indication that the station selector switches at one station corresponding to the other have been operated.

31. In a multiple station communication system, the combination including, signal lights at each station corresponding to other stations in the system station selector switches at each station corresponding to other stations in the system, and means including power supplying means and power and signal light circuits between the stations and power and light circuit controlling switches operable with the selector switches for producinga steady glow of the light at the 35 called station corresponding to the calling sta-' tion upon operation of the called station selector switch at the calling station and for producing a steady glow of the called station light at the calling station upon operation of the calling station selector switch at the called station, thereby to give a positive indication that the station selector switches at one station corresponding to the other have been operated, said circuits and circuit controlling switches also being constructed and arranged to produce flashing of a light corresponding to a called one of the first two stations at another station when the station selector switch at the other station corresponding to one of said two stations has been operated to select it and steady glow of the light at the called one of the first two stations corresponding to the other station.

32. In signaling apparatus for use in communication systems of the type having station selector switches, the combination including, normally inoperative flasher type means adapted when rendered operative to produce a periodically recurring signal voltage, switch means operable with the selector switches normally connecting said voltage producing means to signal circuits individual to the selector switches, and

means including other'switch means operable with said selector switches for rendering operative said voltage producing means when the selector switches are operated to select a station,

v whereby said periodically recurring signal voltage is applied to signal circuits corresponding to nonoperated selector switches.

RICHARD H. CAhdPBELL. 

